Converter optical system

ABSTRACT

A converter optical system includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having positive refractive power; a fourth lens having negative refractive power; and a fifth lens having positive refractive power; wherein the first to fifth lenses are sequentially disposed in numerical order from the first lens to the fifth lens from an object side of the converter optical system to an image side of the optical converter system; and the fourth lens is bonded to either one or both of the third lens and the fifth lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication No. 10-2016-0009794 filed on Jan. 27, 2016, in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND

1. Field

This application relates to a converter optical system.

2. Description of Related Art

A small camera module mounted in a portable terminal is very small. Thesmall camera module has a fixed focus, and may thus image only a subjectpositioned at a short distance therefrom. Some small camera modules mayimage a subject positioned at a far distance therefrom through a digitalzoom function or an optical zoom function. However, the digital zoomfunction has a very low level of resolution, and the optical zoomfunction has a difficulty in obtaining a desired zoom ratio due to alimitation of sizes of portable terminals.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, a converter optical system includes a first lenshaving positive refractive power; a second lens having negativerefractive power; a third lens having positive refractive power; afourth lens having negative refractive power; and a fifth lens havingpositive refractive power; wherein the first to fifth lenses aresequentially disposed in numerical order from the first lens to thefifth lens from an object side of the converter optical system to animage side of the optical converter system; and the fourth lens isbonded to either one or both of the third lens and the fifth lens.

A zoom magnification of the converter optical system may be two times ormore.

An expression 26<D<45 mm may be satisfied, where D is a distance from anobject-side surface of the first lens to an image-side surface of thefifth lens.

An expression 1.55<n1<1.65 may be satisfied, where n1 is a refractiveindex of the first lens.

An expression f number<2.0 may be satisfied, where f number is an fnumber of the converter optical system.

An object-side surface of the first lens may be convex.

An image-side surface of the first lens may be concave.

An object-side surface of the second lens may be convex.

An image-side surface of the second lens may be concave.

Both an object-side surface and an image-side surface of the fourth lensmay be concave.

An object-side surface of the fifth lens may be convex.

In another general aspect, a converter optical system includes a firstlens having positive refractive power; a second lens having refractivepower; a third lens having a convex object-side surface and a conveximage-side surface; a fourth lens having a concave object-side surfaceand a concave image-side surface; and a fifth lens having refractivepower; wherein the first to fifth lenses are sequentially disposed innumerical order from the first lens to the fifth lens from an objectside of the converter optical system to an image side of the converteroptical system; and the image-side surface of the third lens is bondedto the object-side surface of the fourth lens.

The first to fifth lenses may be plastic lenses.

An expression 1000<f/D may be satisfied, where f is an overall focallength of the converter optical system, and D is a distance from anobject-side surface of the first lens to an image-side surface of thefifth lens.

Absolute values of effective radii of the first to fifth lenses maydecrease as a distance of a lens from the object side of the converteroptical system increases so that an expression |r1|>|r2|>|r3|>|r4|>|r5|is satisfied, where r1 is the effective radius of the first lens, r2 isthe effective radius of the second lens, r3 is the effective radius ofthe third lens, r4 is the effective radius of the fourth lens, and r5 isthe effective radius of the fifth lens.

In another general aspect, a converter optical system includes a firstlens having positive refractive power; a second lens having negativerefractive power; a third lens having positive refractive power; afourth lens having negative refractive power; and a fifth lens havingpositive refractive power; wherein the first to fifth lenses aresequentially disposed in numerical order from the first lens to thefifth lens from an object side of the converter optical system to animage side of the optical converter system; and any one or anycombination of any two or more of the following expressions aresatisfied: 26<D<45 mm, 1.55<n1<1.65, f number<2.0, and 1000<f/D, where Dis a distance from an object-side surface of the first lens to animage-side surface of the fifth lens, n1 is a refractive index of thefirst lens, f number is an f number of the converter optical system, andf is an overall focal length of the converter optical system.

Absolute values of effective radii of the first to fifth lenses maydecrease as a distance of a lens from the object side of the converteroptical system increases so that an expression |r1|>|r2|>|r3|>|r4|>|r5|is satisfied, where r1 is the effective radius of the first lens, r2 isthe effective radius of the second lens, r3 is the effective radius ofthe third lens, r4 is the effective radius of the fourth lens, and r5 isthe effective radius of the fifth lens.

An image-side surface of the first lens may be concave.

An object-side surface of the fourth lens may be concave.

An image-side surface of the fifth lens may be convex.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view of a first example of a converter optical system.

FIG. 2 illustrates examples of aberration curves of the converteroptical system illustrated in FIG. 1.

FIG. 3 is a table listing examples of characteristics of lenses of theconverter optical system illustrated in FIG. 1.

FIG. 4 is a table listing examples of aspherical characteristics of theconverter optical system illustrated in FIG. 1.

FIG. 5 is a view of a second example of a converter optical system.

FIG. 6 illustrates examples of aberration curves of the converteroptical system illustrated in FIG. 5.

FIG. 7 is a table listing examples of characteristics of lenses of theconverter optical system illustrated in FIG. 5.

FIG. 8 is a table listing examples of aspherical characteristics of theconverter optical system illustrated in FIG. 5.

FIG. 9 is a view of a third example of a converter optical system.

FIG. 10 illustrates examples of aberration curves of the converteroptical system illustrated in FIG. 9.

FIG. 11 is a table listing examples of characteristics of lenses of theconverter optical system illustrated in FIG. 9.

FIG. 12 is a table listing examples of aspherical characteristics of theconverter optical system illustrated in FIG. 9.

FIG. 13 is a rear perspective view of an example of a portable terminalin which an example of a converter optical system described in thisapplication is mounted.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art may be omitted forincreased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

In this application, a first lens is a lens closest to an object (or asubject), while a fifth lens is a lens closest to an imaging plane (oran image sensor). In addition, all radii of curvature and thicknesses oflenses, D, and focal lengths are represented in millimeters (mm).Further, thicknesses of the lenses, gaps between the lenses, and D aredistances on optical axes of the lenses. Further, in a description ofshapes of the lenses, a statement that one surface of a lens is convexmeans that an optical axis portion of a corresponding surface is convex,and a statement that one surface of a lens is concave means that anoptical axis portion of a corresponding surface is concave. Therefore,even if one surface of a lens is described as being convex, an edgeportion of the lens may be concave. Likewise, even if one surface of alens is described as being concave, an edge portion of the lens may beconvex.

In addition, an object-side surface of each lens is a surface of thecorresponding lens closest to an object, while an image-side surface ofeach lens is a surface of the corresponding lens closest to an imagingplane.

Next, a configuration of a converter optical system will be described.

The converter optical system includes a plurality of lenses. Forexample, the converter optical system may include five lenses. First tofifth lenses constituting the converter optical system are sequentiallydisposed in numerical order from the first lens to the fifth lens froman object side of the converter optical system to an image side of theconverter optical imaging system. For example, the first lens is a lensclosest to the object side, while the fifth lens is a lens closest to aportable terminal in which the converter optical system is mounted.

At least one of the first to fifth lenses may have an aspherical shape.For example, only the fifth lens of the first to fifth lenses may havean aspherical shape. In addition, at least one surface of all of thefirst to fifth lenses may be aspherical. An aspherical surface of eachlens may be represented by the following Equation 1:

$\begin{matrix}{Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10} + {Er}^{12} + {Fr}^{14} + {Gr}^{16} + {Hr}^{18} + {Jr}^{20}}} & (1)\end{matrix}$

In Equation 1, c is an inverse of a radius of curvature of the lens, kis a conic constant, r is a distance from a certain point on anaspherical surface of the lens to an optical axis, A to J are asphericalconstants, and Z is a distance between the certain point on theaspherical surface of the lens at the distance Y and a tangential planemeeting the apex of the aspherical surface of the lens.

Next, the five lenses constituting the converter optical system will bedescribed in detail.

The first lens has refractive power. For example, the first lens mayhave positive refractive power.

At least one surface of the first lens may be convex. For example, anobject-side surface of the first lens may be convex.

The first lens may have a spherical surface. For example, both surfacesof the first lens may be spherical. The first lens may be formed of amaterial having high light transmissivity and excellent workability. Forexample, the first lens may be formed of plastic. However, a material ofthe first lens is not limited to plastic. For example, the first lensmay be formed of glass.

The second lens has refractive power. For example, the second lens mayhave negative refractive power.

The second lens may have a meniscus shape. For example, an object-sidesurface of the second lens may be convex, and an image-side surface ofthe second lens may be concave.

The second lens may have an aspherical surface. For example, anobject-side surface and the image-side surface of the second lens may beaspherical. The second lens may be formed of a material having highlight transmissivity and excellent workability. For example, the secondlens may be formed of plastic. However, a material of the second lens isnot limited to plastic. For example, the second lens may also be formedof glass.

The second lens may be formed of a material having a high refractiveindex. For example, a refractive index of the second lens may be 1.60 ormore. The second lens may have a low Abbe number. For example, an Abbenumber of the second lens may be 30 or less. The second lens configuredas described above improves chromatic aberration produced by the firstlens.

The third lens has refractive power. For example, the third lens mayhave positive refractive power.

At least one surface of the third lens may be convex. For example, bothsurfaces of the third lens may be convex.

The third lens may have a spherical surface. For example, both surfacesof the third lens may be spherical. The third lens may be formed of amaterial having high light transmissivity and excellent workability. Forexample, the third lens may be formed of plastic. However, a material ofthe third lens is not limited to plastic. For example, the third lensmay be formed of glass.

The third lens may be formed of a material having a high refractiveindex. For example, a refractive index of the third lens may be 1.60 ormore. The third lens may have a low Abbe number. For example, an Abbenumber of the third lens may be 32 or less.

The fourth lens has refractive power. For example, the fourth lens mayhave negative refractive power.

The fourth lens may have a biconcave shape. For example, both surfacesof the fourth lens may be concave.

The fourth lens may have a spherical surface. For example, both surfacesof the fourth lens may be spherical. The fourth lens may be formed of amaterial having high light transmissivity and excellent workability. Forexample, the fourth lens may be formed of plastic. However, a materialof the fourth lens is not limited to plastic. For example, the fourthlens may be formed of glass.

The fourth lens may be formed of a material having a high refractiveindex. For example, a refractive index of the fourth lens may be 1.90 ormore. The fourth lens may have a low Abbe number. For example, an Abbenumber of the fourth lens may be 30 or less.

The fourth lens may be bonded to either one or both of the third lensand the fifth lens. For example, an object-side surface of the fourthlens may be bonded to an image-side surface of the third lens, or animage-side surface of the fourth lens may be bonded to an object-sidesurface of the fifth lens, or both the object-side surface of the fourthlens may be bonded to the image-side surface of the third lens and theimage-side surface of the fourth lens may be bonded to the object-sidesurface of the fifth lens.

The fifth lens has refractive power. For example, the fifth lens mayhave positive refractive power.

At least one surface of the fifth lens may be convex. For example, theobject-side surface of the fifth lens may be convex.

The fifth lens may have a spherical surface or an aspherical surface.For example, both surfaces of the fifth lens may be spherical oraspherical. The fifth lens may be formed of a material having high lighttransmissivity and excellent workability. For example, the fifth lensmay be formed of plastic. However, a material of the fifth lens is notlimited to plastic. For example, the fifth lens may be formed of glass.

The converter optical system may satisfy the following ConditionalExpressions:

26<D<45 mm

1.55<n1<1.65

f-number<2.0

1000<f/D

In the above Conditional Expressions, D is a distance from theobject-side surface of the first lens to the image-side surface of thefifth lens, n1 is a refractive index of the first lens, f-number is anf-number of the converter optical system, and f is an overall focallength of the converter optical system.

A converter optical system satisfying the above Conditional Expressionsmay be miniaturized. In addition, a converter optical system satisfyingthe above Conditional Expressions may clearly image a subject positionedat a long distance.

Next, converter optical systems according to several examples will bedescribed.

First, a converter optical system according to a first example will bedescribed with reference to FIG. 1.

The converter optical system 100 according to the first example includesa plurality of lenses having refractive power. For example, theconverter optical system 100 includes a first lens 110, a second lens120, a third lens 130, a fourth lens 140, and a fifth lens 150.

In the first example, the first lens 110 has positive refractive power,and an object-side surface thereof is convex and an image-side surfacethereof is concave. The second lens 120 has negative refractive power,and an object-side surface thereof is convex and an image-side surfacethereof is concave. The third lens 130 has positive refractive power,and both an object-side surface and an image-side surface thereof areconvex. The fourth lens 140 has negative refractive power, and both anobject-side surface and an image-side surface thereof are concave. Thefifth lens 150 has positive refractive power, and an object-side surfacethereof is convex and an image-side surface thereof is concave.

Absolute values of effective radii of the first to fifth lenses 110 to150 decrease as a distance of a lens from an object side of theconverter optical system 100 increases. For example, in the converteroptical system 100, the absolute value of the effective radius of thefirst lens 110 is the largest, and the absolute value of the effectiveradius of the fifth lens 150 is the smallest. That is, a conditionalexpression |r1|>|r2|>|r3|>|r4|>|r5| is satisfied, where r1 is theeffective radius of the first lens 110, r2 is the effective radius ofthe second lens 120, r3 is the effective radius of the third lens 130,r4 is the effective radius of the fourth lens 140, and r5 is theeffective radius of the fifth lens 150.

The fourth lens 140 is bonded to a lens adjacent thereto. For example,the object-side surface of the fourth lens 140 is bonded to theimage-side surface of the third lens 130. Bonded portions of the lensesmay be limited to optical axis centers of the lenses. For example, anedge of the object-side surface of the fourth lens 140 and an edge ofthe image-side surface of the third lens 130 may not be completelybonded to each other.

FIG. 2 illustrates examples of aberration characteristics of theconverter optical system 100 illustrated in FIG. 1. FIG. 3 is a tablelisting examples of characteristics of lenses of the converter opticalsystem 100 illustrated in FIG. 1. FIG. 4 is a table listing examples ofaspherical characteristics of the converter optical system 100illustrated in FIG. 1.

A converter optical system according to a second example will bedescribed with reference to FIG. 5.

The converter optical system 200 according to the second exampleincludes a plurality of lenses having refractive power. For example, theconverter optical system 200 includes a first lens 210, a second lens220, a third lens 230, a fourth lens 240, and a fifth lens 250.

In the second example, the first lens 210 has positive refractive power,and an object-side surface thereof is convex and an image-side surfacethereof is concave. The second lens 220 has negative refractive power,and an object-side surface thereof is convex and an image-side surfacethereof is concave. The third lens 230 has positive refractive power,and both an object-side surface and an image-side surface thereof areconvex. The fourth lens 240 has negative refractive power, and both anobject-side surface and an image-side surface thereof are concave. Thefifth lens 250 has positive refractive power, and both an object-sidesurface an image-side surface thereof are convex.

Absolute values of effective radii of the first to fifth lenses 210 to250 decrease as a distance of a lens from the object side of theconverter optical system 200 increases. For example, in the converteroptical system 200, the absolute value of the effective radius of thefirst lens 210 is the largest, and the absolute value of the effectiveradius of the fifth lens 250 is the smallest. That is, the conditionalexpression |r1|>|r2|>|r3|>|r4|>|r5| is satisfied, where r1 is theeffective radius of the first lens 210, r2 is the effective radius ofthe second lens 220, r3 is the effective radius of the third lens 230,r4 is the effective radius of the fourth lens 240, and r5 is theeffective radius of the fifth lens 250.

The fourth lens 240 is bonded to a lens adjacent thereto. For example,the object-side surface of the fourth lens 240 is bonded to theimage-side surface of the third lens 230. Bonded portions of the lensesmay be limited to optical axis centers of the lenses. For example, anedge of the object-side surface of the fourth lens 240 and an edge ofthe image-side surface of the third lens 230 may not be completelybonded to each other.

FIG. 6 illustrates examples of aberration characteristics of theconverter optical system 200 illustrated in FIG. 5. FIG. 7 is a tablelisting examples of characteristics of lenses of the converter opticalsystem 200 illustrated in FIG. 5. FIG. 8 is a table listing examples ofaspherical characteristics of the converter optical system 200illustrated in FIG. 5.

A converter optical system according to a third example will bedescribed with reference to FIG. 9.

The converter optical system 300 according to the third example includesa plurality of lenses having refractive power. For example, theconverter optical system 300 includes a first lens 310, a second lens320, a third lens 330, a fourth lens 340, and a fifth lens 350.

In the third example, the first lens 310 has positive refractive power,and an object-side surface thereof is convex and an image-side surfacethereof is concave. The second lens 320 has negative refractive power,and an object-side surface thereof is convex and an image-side surfacethereof is concave. The third lens 330 has positive refractive power,and both an object-side surface and an image-side surface thereof areconvex. The fourth lens 340 has negative refractive power, and both anobject-side surface and an image-side surface thereof are concave. Thefifth lens 350 has positive refractive power, and both an object-sidesurface and an image-side surface thereof are convex.

Absolute values of effective radii of the first to fifth lenses 310 to350 decrease as a distance of a lens from the object side of theconverter optical system 300 increases. For example, in the converteroptical system 300, the absolute value of the effective radius of thefirst lens 310 is the largest, and the absolute value of the effectiveradius of the fifth lens 350 is the smallest. That is, the conditionalexpression |r1|>|r2|>|r3|>|r4|>|r5| is satisfied, where r1 is theeffective radius of the first lens 310, r2 is the effective radius ofthe second lens 320, r3 is the effective radius of the third lens 330,r4 is the effective radius of the fourth lens 340, and r5 is theeffective radius of the fifth lens 350.

The fourth lens 340 is bonded to a lens adjacent thereto. For example,the object-side surface of the fourth lens 340 is bonded to theimage-side surface of the third lens 330. Bonded portions of the lensesmay be limited to optical axis centers of the lenses. For example, anedge of the object-side surface of the fourth lens 340 and an edge ofthe image-side surface of the third lens 330 may not be completelybonded to each other.

FIG. 10 illustrates examples of aberration characteristics of theconverter optical system 300 illustrated in FIG. 9. FIG. 11 is a tablelisting examples of characteristics of lenses of the optical convertersystem 300 illustrated in FIG. 9. FIG. 12 is a table listing examples ofaspherical characteristics of the converter optical system 300illustrated in FIG. 9.

Table 1 below lists optical characteristics and values of ConditionalExpressions of the converter optical systems 100, 200, and 300 accordingto the first, second, and third examples. An overall focal length (f) ofthe converter optical system is substantially determined to be 40000 ormore. In the converter optical system, a focal length (f1) of the firstlens is substantially determined to be in a range of 35.0 to 72.0. Inthe converter optical system, a focal length (f2) of the second lens issubstantially determined to be in a range of −34.0 to −64.0. In theconverter optical system, a focal length (f3) of the third lens issubstantially determined to be in a range of 8.0 to 17. In the converteroptical system, a focal length (f4) of the fourth lens is substantiallydetermined to be in a range of −6.0 to −2.0. In the converter opticalsystem, a focal length (f5) of the fifth lens is substantiallydetermined to be in a range of 5.0 to 10. In the converter opticalsystem, a distance (D) from the object-side surface of the first lens tothe image-side surface of the fifth lens is substantially determined tobe in a range of 26 to 45.

TABLE 1 Characteristic First Example Second Example Third Example f48328.0 47047.3 47120.4 f1 69.8771 44.3692 36.7307 f2 −62.6374 −44.0214−35.7526 f3 15.9998 9.8516 9.5286 f4 −4.4239 −3.2493 −3.0349 f5 8.43967.5096 6.5519 D 40.00 30.91 26.97 n1 1.5891 1.5891 1.5891 f-number 1.951.93 1.94 f/D 1208.2 1522.1 1747.1

FIG. 13 is a rear perspective view of an example of a portable terminalin which an example of a converter optical system described in thisapplication is mounted.

The converter optical system 100 described above is mounted in aportable terminal 200. For example, the converter optical system 100 iscoupled to a camera module 210 embedded in a front surface or a rearsurface of the portable terminal 200.

The converter optical system 100 improves a zoom magnification of thecamera module 210. For example, the converter optical system 100increases a focal length of the camera module 210 by two or more times.That is, the converter optical system 100 provides a telephoto lensfunction. Therefore, when the converter optical system 100 is used, asubject positioned at a long distance may be clearly imaged.

Although the example in FIG. 13 shows the converter optical system 100described above being mounted in the portable terminal 200, this ismerely an example, and either the converter optical system 200 or theconverter optical system 300 described above, or another converteroptical system satisfying the Conditional Expressions described above,may be mounted in the portable terminal 200.

According to the examples described above, a converter optical systemproviding a telephoto lens function may be provided.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. A converter optical system comprising: a firstlens having positive refractive power; a second lens having negativerefractive power; a third lens having positive refractive power; afourth lens having negative refractive power; and a fifth lens havingpositive refractive power; wherein the first to fifth lenses aresequentially disposed in numerical order from the first lens to thefifth lens from an object side of the converter optical system to animage side of the optical converter system; and the fourth lens isbonded to either one or both of the third lens and the fifth lens. 2.The converter optical system of claim 1, wherein a zoom magnification ofthe converter optical system is two times or more.
 3. The converteroptical system of claim 1, wherein an expression 26<D<45 mm issatisfied, where D is a distance from an object-side surface of thefirst lens to an image-side surface of the fifth lens.
 4. The converteroptical system of claim 1, wherein an expression 1.55<n1<1.65 issatisfied, where n1 is a refractive index of the first lens.
 5. Theconverter optical system of claim 1, wherein an expression f-number <2.0is satisfied, where f-number is an f-number of the converter opticalsystem.
 6. The converter optical system of claim 1, wherein anobject-side surface of the first lens is convex.
 7. The converteroptical system of claim 1, wherein an image-side surface of the firstlens is concave.
 8. The converter optical system of claim 1, wherein anobject-side surface of the second lens is convex.
 9. The converteroptical system of claim 1, wherein an image-side surface of the secondlens is concave.
 10. The converter optical system of claim 1, whereinboth an object-side surface and an image-side surface of the fourth lensare concave.
 11. The converter optical system of claim 1, wherein anobject-side surface of the fifth lens is convex.
 12. A converter opticalsystem comprising: a first lens having positive refractive power; asecond lens having refractive power; a third lens having a convexobject-side surface and a convex image-side surface; a fourth lenshaving a concave object-side surface and a concave image-side surface;and a fifth lens having refractive power; wherein the first to fifthlenses are sequentially disposed in numerical order from the first lensto the fifth lens from an object side of the converter optical system toan image side of the converter optical system; and the image-sidesurface of the third lens is bonded to the object-side surface of thefourth lens.
 13. The converter optical system of claim 12, wherein thefirst to fifth lenses are plastic lenses.
 14. The converter opticalsystem of claim 12, wherein an expression 1000<f/D is satisfied, where fis an overall focal length of the converter optical system, and D is adistance from an object-side surface of the first lens to an image-sidesurface of the fifth lens.
 15. The converter optical system of claim 12,wherein absolute values of effective radii of the first to fifth lensesdecrease as a distance of a lens from the object side of the converteroptical system increases so that an expression |r1|>|r2|>|r3|>|r4|>|r5|is satisfied, where r1 is the effective radius of the first lens, r2 isthe effective radius of the second lens, r3 is the effective radius ofthe third lens, r4 is the effective radius of the fourth lens, and r5 isthe effective radius of the fifth lens.
 16. A converter optical systemcomprising: a first lens having positive refractive power; a second lenshaving negative refractive power; a third lens having positiverefractive power; a fourth lens having negative refractive power; and afifth lens having positive refractive power; wherein the first to fifthlenses are sequentially disposed in numerical order from the first lensto the fifth lens from an object side of the converter optical system toan image side of the optical converter system; and any one or anycombination of any two or more of the following expressions aresatisfied:26<D<45 mm,1.55<n1<1.65,f-number<2.0, and1000<f/D, where D is a distance from an object-side surface of the firstlens to an image-side surface of the fifth lens, n1 is a refractiveindex of the first lens, f-number is an f-number of the converteroptical system, and f is an overall focal length of the converteroptical system.
 17. The converter optical system of claim 16, whereinabsolute values of effective radii of the first to fifth lenses decreaseas a distance of a lens from the object side of the converter opticalsystem increases so that an expression |r1|>|r2|>|r3|>|r4|>|r5| issatisfied, where r1 is the effective radius of the first lens, r2 is theeffective radius of the second lens, r3 is the effective radius of thethird lens, r4 is the effective radius of the fourth lens, and r5 is theeffective radius of the fifth lens.
 18. The converter optical system ofclaim 16, wherein an image-side surface of the first lens is concave.19. The converter optical system of claim 16, wherein an object-sidesurface of the fourth lens is concave.
 20. The converter optical systemof claim 16, wherein an image-side surface of the fifth lens is convex.